As is known, solid propellant motors are used both in the military field and in the field of space launchers.
In both applications, the known motors comprise an outer casing, which houses a predefined annular mass of solid propellant and is closed at the opposite ends by two closing heads distinct from the casing.
One of said heads carries an ignition device for igniting the solid propellant while the other supports a nozzle for outlet of the exhaust gases resulting from combustion of the propellant inside the casing.
Loading of the solid propellant in the casing, assembly of the heads and connection of the heads to the casing and any subsequent storage are generally performed in sites or on different platforms normally well away from the launch platform.
Both in the storage period and during transport towards the launch platform and in any case for the entire launch preparation phase on the same platform, external causes such as an increase in temperature, an impact or an electrostatic discharge, for example, can cause a sudden and uncontrolled ignition of the solid fuel with devastating effects in terms of financial losses or loss of human life. For this reason, the heads are initially coupled to the casing by means of distinct temporary connecting elements with predefined breaking points which, in the event of spontaneous ignition, rupture due to the action generated by the pressure of the gases inside the casing, permitting an increase in the outflow section of the gases towards the outside. This reduces the pressure inside the motor combustion chamber and, consequently, the thrust generated.
When all the preparatory operations have been positively completed on the launch platform, the temporary connecting elements are removed and replaced with permanent structural elements which permanently connect the heads to the casing, enabling the motor for flight.
The removal of the temporary connecting elements and assembly of the permanent ones involves complications and obliges the technicians in charge to work in difficult conditions exposed to risks.
A condition of safety at spontaneous ignition is never fully achieved when several motors are stacked on top of one another, as in the case of multistage launchers. In said cases, in fact, the permanent connecting elements must be inserted before stacking one motor on top of the motor below which, at this point, is ready for ignition and therefore has the same problems as described before concerning prevention of the effects of spontaneous ignition.
A propeller with closing heads screwed on the ends of an intermediate tubular body is described in JP document S 604 78 52.